This invention relates to apparatus for use in artifical respiration, and particularly to intratracheal tubes used during surgical procedures and in ventilatory support of critically ill patients.
Modern respiratory support of patients and modern anesthesia procedures often require administration of air, oxygen or other gases into the lungs under positive pressure, as provided by apparatus such as respirators, anesthesia machines, or manually compressed balloons. For conducting the gas to a patient's lungs, a tube is generally inserted into the trachea either through the mouth, the nose, or via a surgically created opening in the neck in a tracheostomy procedure; the corresponding intratracheal tubes for the above intubations are referred to as endotracheal, nasotracheal or tracheostomy tubes. A pulsating supply of the pressurized gas from an external source is directed down through the intratracheal tube where it forces a rhythmic expansion of the lungs. Such intubation is especially advantageous when a patient is unable to provide even the minimum muscular activity to sustain breathing.
The typical intratracheal tube has an outer diameter smaller than the inside diameter of the tracheal passage into which it is inserted which facilitates the intubation, but results in an annular space between the tube and the inner lining of the trachea. In order to artifically inflate the lungs with positive pressure, an air-tight seal must be established in this annular space, or else air pumped down the tube toward the lungs will escape upward through this space. Conventional means for achieving such a seal include various inflatable "cuffs", which have appearance similar to miniature inflated inner-tubes for tires. Such a cuff is attached to and surrounds a tube, and when inflated the cuff extends radially outward from the tube until it contacts the tracheal wall, thus filling the annular space. A cuff is inflated only after its tube is inserted into the trachea, and then by injection of air, gas or other fluid through a small conduit. An additional important reason for the above-described cuff seal is the prevention of aspiration, i.e. the passage through this annular space into the lungs of liquids or solids from the upper airway or from the mouth. This problem is particularly serious with unconscious patients who may tend to aspirate vomited material or other oral secretions.
In recent years it has become evident that tracheal walls have been damaged by an inflated cuff, where the lateral pressure exerted by the cuff against the mucosal lining of the trachea was prolonged and/or excessive. The recent medical literature is replete with studies and surveys of tracheal stenosis, tracheomalacia, ulceration, erosion of the tracheal wall, and the formation of lesions resulting from the prolonged intubation with intratracheal tubes. In the vast majority of such complicating diseases and injuries, which are often worse than the respiratory illness itself or other original cause for using the intratracheal tube, the cause of said secondary problems has been traced directly to the employment of the cuff and the prolonged tracheal wall pressure required for its use. A partial tabulation of such studies, includes the following articles: Carrol and Hedden, Journal of Anesthesiology, September, 1969, Vol. 31, No. 3, pages 275 - 281; Catane et al, British Journal of Anaesthesiology, 1969 Vol. 41, page 1086; Grillo, H.C. Journal of Thoracic and Cardiovascular Surgery, January 1969, Vol. 57, No. 1 page 52; Shelly et al. Journal of Thoracic and Cardiovascular Surgery, May 1969, Vol. 57, No. 5 page 623; Fishman et al. Annals of Thoracic Surgery, July 1969, Vol. 8, No. 1, page 47; Miller et al. Annals of Surgery, Feb. 1970, Vol. 171, No. 2, page 283; and Westgate et al. Anesthesia and Analgesia, May-June 1970, Vol. 49, No. 3, page 393.
The results of the studies and findings in this field lead to the conclusion, that while intratracheal support of ventilation is often necessary, there is a need for an improved, less harmful intratracheal tube with means for occluding the tracheal passage, and efforts in this direction have produced further analytical data on the mechanical operation of these devices. As indicated above conventional cuffs require pressures and volumes of substantially high magnitude to produce sufficient lateral or tracheal wall pressure to maintain the cuff in sealing condition against the wall of the trachea. This lateral pressure is at least equal to the highest peak pressure reached in the lungs below the cuff during the artifical inflation of said lungs. Consequently, with these conventional cuffs, the tracheal wall pressure becomes generally significantly greater than the pressure sustaining capillary blood flow, so that blockage of blood flow through the mucous lining (ischemia) occurs. Not even the standard procedure of deflating the cuff for a few minutes or so every hour successfully overcomes this problem.
The above problems are accentuated when one appreciates the fact that since the intubation is hidden from view of the doctor or surgeon, accurate measurement of the pressure is not feasible. It is thus not uncommon, in order to insure an airtight seal, that an operator will set the cuff and tracheal wall pressure at levels greater than that actually necessary for the secure occlusion of the trachea.
With the hope of decreasing the lateral pressure against the tracheal wall, certain parachute or canopy shaped cuffs have been developed which differ from "inner tube" or "balloon" cuffs in that they do not require external inflation, i.e. from a source of air under pressure. In place of the balloon is a parachute-like member with its open end directed downward and its dome traversed by the tube extending axially therethrough. An air flow, during the positive pressure phase of respiration, downward through the tube and tending to escape upward via the annular space in the tracheal passage, will collect under the parachute dome, and inflate same until the body of the parachute is distended into pressure contact with the tracheal lining. The degree of distention depends on the volume and pressure of this upward gas flow; however, the lateral pressure which these cuffs exert on the tracheal wall is no greater than, and virtually equals the pressure which exists in the airway below or distal to the cuff at any given moment. Accordingly the duration and magnitude of this pressure is only the minimum required for achieving the airway seal, as contrasted to an arbitrary high pressure of balloon cuffs inflated from an independent and external source. Thus with these parachute cuffs it is essentially impossible to injudiciously or accidentally overinflate, since the external gas source has been eliminated. Illustrations and further description of these earlier parachute cuffs are found in the U.S. Pat. No. 3,769,983 issued on Nov. 6, 1973 to A.D. Merav, the inventor in the present application, and in article "Pressures of Tracheostomy Cuffs in Ventilated Patients", New York Journal of Medicine, Aug. 15, 1971, p.p. 1923-1928.
Unfortunately these parachute-type cuffs are not totally satisfactory. While they achieve an airway seal under conditions of positive-pressure ventilation, and are especially well-suited for prolonged intubation in patients who are conscious and do not tend to aspirate, they do not seal the airway when the patient breathes in spontaneously, at which time he may aspirate liquids or solids. Because of this real and frequent danger with these known parachute cuffs, many surgeons are reluctant or simply refuse to use them, and instead use the standard balloon cuffs with their inherent disadvantages.
It is an object of the present invention to provide an occulusive intratracheal cuff which can create an airway seal that is continuous and sufficient to prevent aspiration, and yet will not exert a continuous high pressure against the tracheal wall, and will thus eliminate the ancillary problems caused by said excessive tracheal wall pressure common with use of balloon cuffs.